1. Field of the Invention:
This invention relates to an ink ribbon cassette for use with an impact printer, more particularly to such an ink ribbon cassette having teeth for feeding an ink ribbon mounted in the ink ribbon cassette.
2. Description of the Prior Art:
U.S. Pat. No. 4,552,469 discloses an ink dot printer having an ink cartridge and an ink tank. Magnetic ink is filled into the ink cartridge. A slit in the ink cartridge and a connecting hole communicate with each other. The magnetic ink flows from the ink cartridge. When a main switch is turned on, the magnetic ink is absorbed in a slit provided between front end portions to thereby define a magnetic ink film. When a tip end of a needle projects to the magnetic ink film, the magnetic ink is applied to the tip end and is supplied to a surface of a recording paper. Upon selectively driving the needle, characters and numerals are visibly formed on the surface of the recording paper. The ink supplied to the tip end of the needle thus is consumed. Magnetic ink is newly supplied from the ink tank to the tip end of the needle upon completion of the series of operations set forth above. U.S. Pat. No. 4,552,469 discloses a plurality of dot characters and numerals being printed in succession, but does not teach a concept of printing by the needle via the ink ribbon by transferring the ink to the ribbon. Such patent discloses that the ink film between the front end portions is directly delivered to the recording paper via the needle, but there is no description of extending the life cycle of the ink ribbon.
Another prior art arrangement is shown in Japanese utility model Ser. No. 58-25727 filed Feb. 25, 1983 (laid-open publication No. 59-131851) in the name of Yoshinori Koshida and Kenji Kanabo for an invention entitled RIBBON CARTRIDGE. Koshida et al disclose a ribbon cartridge having an ink supply roller absorbing ink. The ink supply roller and a ribbon feed drive roller are in contact with each other and thereby allow ink to be transferred to a ribbon feed surface of the ribbon feed drive roller in response to rotation thereof. The ink supply roller moves very slowly and approaches the ribbon feed drive roller in proportion to the rotation of the ribbon feed drive roller by the action of gears and a cam, for thereby allowing the ink supply roller to be depressed gradually by a high pressure. Thus, the ink absorbed in the ink supply roller is gradually squeezed and transferred to the ribbon drive roller. The ink attached to the surface of the ribbon drive roller is transferred to an ink ribbon when the ink ribbon is held between the ribbon drive roller and a ribbon feed driven roller and fed thereby. Hence, the life cycle of the ink ribbon is lengthened. Further, Koshida et al disclose the ribbon feed drive roller comprising a plurality of rollers having the same diameter and integrally fixed to the same shaft at appropriate intervals, and the ribbon feed driven roller comprising rollers the same as those of the ribbon feed drive roller and integrally fixed to another shaft at a location opposite to the feed drive roller. The ribbon is held between the ribbon feed drive roller and the ribbon feed driven roller and is fed therebetween. The ink ribbon of Koshida et al cannot be accurately fed or delivered due to slippage between the ribbon feed drive roller or the ribbon feed driven roller and the ink ribbon upon an increased load. The ink transferred to the ink ribbon is squeezed when a contact pressure sufficient to accurately supply the ink ribbon is applied to the ribbon feed drive roller and the ribbon feed driven roller, even if the load is increased. The squeezed ink overflows to ribbon portions not held between the rollers, thus decreasing the amount of ink to be supplied to the ribbon portion which is held between the rollers. Accordingly, the printing quality is deteriorated since the printing is effected by use of ink which is supplied non-uniformly and since the density of printing is different at various portions of the ribbon.